Fatigue‐Life Prediction of Additively Manufactured Material: Effects of Defect Spacing and Multi‐Site Damage

Fatigue‐life prediction of additively manufactured metals is challenging due to the random distribution of process‐induced defects, whose proximity can significantly influence crack initiation and propagation, and whose multiplicity can promote multi‐site damage. Prediction approaches based on single‐crack growth often overestimate fatigue life by neglecting defect interactions and multi‐site crack propagation, particularly in low cycle fatigue and mid‐life regimes, where crack coalescence and stress field interactions play a crucial role. This study integrates small‐ and large‐crack growth test data with defect characteristics, including size and spacing obtained from X‐ray computed tomography, to estimate the fatigue life of Ti‐6Al‐4V fabricated via laser directed energy deposition. The plasticity‐induced crack closure model, FASTRAN, was employed to simulate crack propagation and compare single‐crack and multi‐crack approaches in fatigue‐life prediction. The multi‐site damage approach, which explicitly accounts for defect spatial distribution through nearest neighbor distance analysis, significantly improves fatigue‐life predictions in low cycle fatigue and mid‐life regimes, demonstrating strong agreement with experimental data.